Various yarn feed units which comprise yarn guides corresponding to each feed station in the machine are already known and in use in circular hosiery machines, including double cylinder machines. The yarn guides are controlled and moved individually between an engaged position close to the cylinder, to deliver yarn to the corresponding needles, and a disengaged position, away from the cylinder, to prevent yarn from being picked up by the needles. This is so that the needles can be fed with yarns of different nature, weight and colour from time to time on the basis of the requirements of the current knitting work. At the present time yarn guides are engaged and disengaged by various means, well known to those skilled in the art, but which are nevertheless relatively complex and cumbersome, given the nature and arrangement of the components of such actuator means.